The published book by Professor A.P. Lebedev is dedicated to a very important period in the history of Byzantium, in the life of the Byzantine and, in general, the Eastern Church. This period is associated with the activities of an outstanding church figure in Byzantine history - Patriarch Photius of Constantinople. The author sets the task of considering the history of the Councils of Constantinople in the mid-9th century. against the backdrop of the struggle between the Western and Eastern churches in this era and the struggle unfolding in the Byzantine Church between supporters of the deposed Patriarch Ignatius and supporters of Photius. The book is an integral part of A.P. Lebedev’s research on the relationship between the two Churches during the period of their division in the 9th–11th centuries. A.P. Lebedev builds his presentation on the basis of a strict analysis of sources. The book will be useful not only to specialists in the field of Byzantine history and Church history, but also to everyone interested in these problems. The publication is supplied with comments, a list of the latest literature, sources, and a name index.